Getting rid of the little (+) buttons for a clean window
2.79


Duplicate the area into a new window.
View ‣ Duplicate Area into new Window
OR
Duplicate a window with &#9096; Ctrl&#9095; AltW
Info area ‣ Window ‣ Duplicate Window
Then, Toggle Area Fullscreen &#9095; AltF10. View ‣ Toggle Fullscreen Area
Eliminiate additional 3D View icons in the User Preferences &#9096; Ctrl&#9095; AltU under Interface ‣ Display (on the left)




2.8

Although the manual says the same as in 2.79. The Toggle Fullscreen Area is somewhere else in 2.8 (2018-10-12).

3D View Menu: View ‣ Area ‣ Toggle Fullscreen Area. &#9096; Ctrl&#9095; AltSpace